This invention relates to over the road vehicles and more particularly to a system for cooling power train liquids such as engine lubricants and transmission oil.
Over the over the road vehicles are often operated under conditions in which engine and transmission oils may become overheated. While historically, properly functioning engine coolant systems maintained engine temperatures and the temperatures of connected transmissions at temperatures which were low enough to avoid significant degradation of engine and transmission oils, such is no longer the case. Cooling systems for vehicle engines in the past maintained the coolant at temperatures of the order of 180xc2x0 F. now the typical minimum temperature. Once pressurized systems were developed maximum coolant temperatures were elevated to 100xc2x0 Centigrade (212xc2x0 F.). In order to improve engine performance and to meet emission control requirements, engine coolants have since come to be maintained at maximum temperatures of the order of 105xc2x0 C. (220xc2x0 F.). Maximum coolant temperatures continue to increase to anticipated, if not already achieved, temperatures of the order of 110xc2x0 C. (230xc2x0 F.) and even higher.
When the temperature of the coolant is elevated, obviously the temperature of the engine itself is elevated and with it the temperature of lubricating and transmission oils. When oil is heated, its viscosity is reduced and with it, its lubricating qualities. Moreover, if the temperature of transmission or lubricating oil is sufficiently elevated, molecular chains of the oil are broken down and the lubricating qualities of the oil can be seriously degraded.
Heat exchangers for cooling engine lubricants with engine coolants are well known. As operating temperatures have elevated, such lubricant cooling systems are, at least in many instances, no longer adequate to maintain the lubricant below an appropriate maximum temperature.
There have been proposals to provide supplemental cooling of lubricating oil through the use of auxiliary heat exchangers connected in series with a primary heat exchanger. With such a proposal, lubricating oil is fed through a series connected heat exchanger when the primary heat exchanger is no longer able to reduce engine oil temperature to a desired operating level.
According to the present invention, a supplemental engine or transmission oil heat exchanger is connected in parallel with a primary heat exchanger. This parallel arrangement has significant advantages over prior proposals for supplemental cooling of engine and transmission oils. The advantages include:
1) The system is easily connected to a conventional engine. This permits a manufacturer to use the same basic engine design for vehicles to be operated at elevated coolant temperatures as is used for vehicles at traditional coolant temperatures.
2) The system permits effective operation at lower oil pressures than are required when the oil to be cooled is being forced through series connected heat exchangers. As a consequence, combined oil pressure drop and the necessarily pump energy to force the oil through the heat exchangers is significantly reduced.
3) The cooling capacity for the oil being cooled and the temperature of it is controlled by a simple restricter/shut-off valve.
4) A low pressure parallel system is safer for the engine in case of leakage. Thus, a xe2x80x9climp homexe2x80x9d function is achieved by shutting off the circuit in the event that there is leakage.
5) A parallel heat exchanger has the ability to cool oil to temperatures well below the temperature exiting an engine coolant heat exchanger permitting the routing of lubricating oil at two different temperatures to different locations in the engine thereby enhancing the lubrication and cooling of the engine.
Accordingly, the objects of the invention are to provide a novel and improved oil cooling system for a vehicle and a process of cooling oil.